[AstroPy] API question: Instantiating of time/coord and similar
perry at stsci.edu
Thu May 3 14:19:19 EDT 2012
I didn't mean to say that it should be mostly or entirely different. I
would like to see a great deal of commonality actually (preferably
sharing the same base class for coordinate transformations for example).
I'd like to expand on what I would like to see, but I'm not sure I
will have time today. Perhaps tomorrow.
On May 3, 2012, at 1:39 PM, David Berry wrote:
> What you say is reasonable, but I don't see that it follows that
> they need to be handled differently. Considered as a class,
> coordinate systems have a lot of common properties and methods no
> matter what they describe. Getting a sufficiently generic base class
> allows you to extend the system easily. That's why it was so easy to
> add support for spectral and time to AST. In practice it all works
> out very smoothly.
> On Thursday, 3 May 2012, Perry Greenfield <perry at stsci.edu> wrote:
> > On May 3, 2012, at 11:45 AM, David Berry wrote:
> >> On 3 May 2012 16:39, Wolfgang Kerzendorf <wkerzendorf at gmail.com>
> >>> Hi all,
> >>> This topic has expanded a lot;-)
> >>> So adressing point 1: Yes, you're technically right. That both
> of these things do coordinate transformations. But there are many
> coordinate transformations in astronomy and in astropy we don't have
> a one-size fits-all mentality about them (in my sense for good
> reason). For example, switching between different units, doppler-
> shifting spectra , etc... all are technically coordinate
> transformations, but we treat them differently and not through one
> coordinate transformer.
> >> Is there a reason for that?
> > I agree that they are both identical in some respects (and it is
> worth considering a common api for at least a good part of both). To
> me the main difference is that one is standards focused (dealing
> with well known coordinate systems and the transformations between
> them, whereas wcs is dealing more with instrumental effects and
> transforming from that to world coordinates (which may be one of the
> standard systems, but it may not). In one most of the transforms are
> simple, as is the geometry. In the other they can be quite complex.
> The former usually transforms few distinct coordinates (yes, you can
> do big catalogs too), and the latter transforms large numbers of
> pixel coordinates in many case.
> > So I'm not surprised that people come from different directions
> when approaching these two issues.
> > Perr
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